High frequency electron discharge device with heat dissipation means



INVENTOIR, STANLEY F. SWIADEK Sept 20,1966 5. F SWIADEK HIGH FREQUENCY ELECTRON DISCHARGE DEVICE WITH HEAT DISSIPATION MEANS Filed March 18. 1963 United States Patent 3,274,429 HKGH FREQUENCY ELEKITRON DISCHARGE DE- VECE WITH HEAT DiiSSllPATllON MEANS Stanley F. Swiadelt, Sunnyvale, Calif., assignor to Varian Associates, Palo Alto, Calif., a corporation of California Filed Mar. 18, 1963, set. No. 265,633 13 Claims. (Cl. 315-36) The present invention relates in general to high frequency tube apparatus and more particularly to improved light weight microwave tube apparatus providing i11- creased power output and stability in adverse environments of shock and vibration. These improved tubes are found to be especially useful as moderate to high power traveling wave tube microwave amplifiers or oscillators in airborne systems.

Heretofore, moderate power traveling wave tubes have been made for airborne service. However these prior tubes have been plagued with several problems. One problem is that the elongated tube envelope, to be replaceable in service must readily slide within an elongated beam focus solenoid. The hollow core of the solenoid was spaced from the tube body to facilitate insertion of the tube and to provide space for input and output R.F. leads. Because of this spacing, conduction cooling from the metallic tube envelope to the solenoid was greatly impaired causing the tube to operate at higher temperatures and reduced power levels as compared to those attainable if conduction cooling could be had from the tube envelope to the beam focus solenoid structure.

A second problem encountered in the prior tubes was encountered due to the fact that the helical slow wave structure was glazed to a plurality of longitudinally directed sapphire support rods over substantially the entire length of the helix. These glazed joints, where the helix made contact with the support rods, absorbs RF. energy from the R.F. wave on the helix and as a consequence, produced heating of the glaze which in turn caused more absorption of RP. energy and heating. As a result such slow wave structures had an upper power limit of approximately 400 watts C.W. with about 25% of the RF. power going for heating of the helix and glaze.

A third problem encountered with a helical slow wave circuit being glazed over its entire length to the support rods carried within a metallic envelope is that unequal thermal expansion of the tube envelope and helix produced fractures of the lead in and out connectors at the input and output terminals of the tube. Assuming a 20 inch length slow wave circuit, during tube processing at 600 C. the metallic envelope, usually stainless steel, expands inch more than the helix, but during tube use at 500 watts C.W. the helix runs at 1500 C. and the envelope much cooler causing the helix to expand about /8 of an inch more than the envelope. This quarter inch expansion differential over-stresses the input connectors producing failure thereof in use.

A fourth problem has been in obtaining eflicient liquid cooling of tube structures using a light weight relatively low pressure supply of liquid coolant. The coolant channels around the collector are typically of uniform cross sectional area producing uniform cooling effect but heating of the collector by beam interception is not uniform thereby producing uneconomical use of the available coolant pressure. In addition the solenoid is typically cooled by coolant channels'series connected with the collector channels and, because of the large differential in thermal expansion between the solenoid and collector in use, the channeling is often fractured rendering the tube inoperative.

In the present invention a novel tube construction is provided which obviates the aforementioned problems. Conduction cooling of the tube body is obtained by packing an ensemble of metallic particles or spheres between the core of the beam focus solenoid and the tube envelope. The packed spheres provide a high thermal conductance path to the solenoid while rigidly supporting the tube body. The helix is severed and glazed to the sapphire support rods substantially only at the central ends of the helices while the support rods are tacked to the envelope at the outermost ends of the severed helices to prevent distortions of the helix due to differential expansion be tween the helix assembly and the tube envelope. This helix support technique avoids fracture of the input and output connectors while permitting higher power levels on the helix by eliminating glaze at the high power end of the helix. The tube solenoid and collector are supplied with liquid coolant flow channeled around the solenoid and collector structure. The coolant channel is reduced in cross sectional area around the mid-section or hottest portion of the collector to speed up the velocity of coolant flow in this region to obtain increased localized cooling. The collector and solenoid coolant channels are series connected via the intermediary of a bellows section of channel to permit large differentials in expansion of the solenoid and collector structures in use without producing leaks in the system of coolant channels.

It is therefore a principal object of this invention to provide a novel microwave tube apparatus having increased power output and stability in adverse environment of shock and vibration.

One feature of the invention is to provide a unique means for supporting slow wave circuits such as, for example, a helix circuit employed in a traveling wave tube.

Another feature of the present invention is the provision of unique, light weight, easily assembled and disassembled cooling apparatus for transferring heat from the main body of a high frequency electron discharge device to the surrounding beam focusing apparatus.

Another feature of the present invention is the provision of liquid cooling means for cooling the main body and collector portion and the focusing means of a high frequency electron discharge device, such as for example, a traveling wave tube, wherein cooling liquid is transferred :between the main body and the collector portion through a flexible conduit which permits differential thermal expansion between the main body portion of the tube and the collector portion over wide variations in environmental temperatures and operating temperatures without cracking and consequent leakage occurring in the liquid cooling system.

Another feature of the present invention is the provision of a collector cooling arrangement utilizing low velocity, low pressure sections, which limit the fluid pressure drop across the tube to a predetermined minimum level while simultaneously employing a high velocity, high pressure intermediate fluid cooling section between the low pressure sections.

These and other features and advantages of the present invention will be more apparent after a perusal of the following specification taken in conjunction with the accompanying drawings, wherein FIG. 1 is a fragmentary longitudinal cross-sectional view of a traveling wave tube incorporating the novel features of the present invention,

FIG. 2 is an enlarged view of the novel slow wave supporting structure of the present invention taken at lines 22 in FIG. 1,

FIG. 3 is a transverse cross sectional view taken along lines 3-3 of FIG. 2 and showing the novel slow wave supporting structure and,

FIG. 4 is a fragmentary enlarged sectional view of the portion of FIG. 1 delineated by lines 44 and showing the pellet-like spherical-shaped balls forming a unique, easily assembled and disassembled heat transfer means of the present invention.

Referring now to the drawings, the traveling wave tube includes a helix slow wave structure 8 comprising a pair of severed sections 9, 10 coaxi-ally disposed within a hollow metallic cylindrical main body shell or barrel 11 preferably of stainless steel and forming a central portion of the tubes vacuum envelope. Each of said several helix sections is supported by means of three equilaterally disposed longitudinally directed dielectric supporting rods 12 preferably of sapphire abutting the interior wall of the cylindrical barrel 11.

A conventional electron gun structure 13 for generation of a preferably hollow cylindrical electron beam is disposed at one end of the slow wave structure. A beam collector 14 preferably of copper is disposed at the other end of the slow wave structure. A pinched-off exhaust tubulation seal 15 terminates the collector.

A cylindrical anode member 16 is secured to one end of the sleeve 11 and surrounds and supports the gun structure 13. Filament leads 17, 18 extend through the vacuum sealed base portion of the gun structure and are embedded within end sealing and insulating mass 19 preferably of silicone rubber. A stepped annular member 20 preferably of copper is secured as by brazing to the collector end of main body barrel 11 and to the collector 14 at enlarged collector portion 21 to thereby complete a vacuum tight envelope. R.F. leads 22, 23 extend from the gun and collector end portions, respectively, of the slow wave structure 8 and form the entrance and exit means for the RF. energy which propagates along the slow wave structure and interacts with the electron beam. The leads 22 and 23 are preferably coaxial conductors and terminate at the collector end of the tube.

Annular flange portion 24 on stepped annular member 20 serves as a sealing and mounting flange for maintaining the traveling wave tube within a solenoidal magnetic focusing means 25. A stepped annular mounting ring 26 is secured to flange 24 at an inner portion thereof as by bolts 24' and secured as by means of bolts 26 or the like to solenoidal pole piece 27 at an outer portion thereof. A suitable organic sealing material such as RTV-60 may be coated on the engaging surfaces 28, 29 to prevent hazardous fumes, such as jet vapor fumes for example, from entering the annular space 30 between main body sleeve 11 and the cylindrical shell 31 forming the interior surface of focusing solenoid 25. Such sealing is necessary to eliminate any possibility of an explosion occurring due to the abovementioned fumes coming in contact with hot spots on the tube shell.

Surrounding the solenoid 25 is a cylindrical exterior tube 32 of cold rolled steel or the like which is attached as by brazing to pole pieces 27, 33. Sleeve 32 is spaced from the exterior surface of solenoid 25 to leave an annular space 34 therebetween. An end plate 35 is bolted or otherwise secured to the gun end of the tube.

A collector cooling assembly 36 comprising an internal annular core member 37, preferably of copper, is brazed or the like to the exterior of the collector. Mounted on core member 37 are front and rear cooler end plates 38, 39, respectively, and exterior annular shell 40 which, together with the enclosed cooling fins, forms a composite liqgiid cooler assembly for the collector portion of the tu e.

A liquid coupling assembly 41 forms a passage for transferring liquid between the annular space 34 surrounding the solenoid and the collector cooler assembly 36. The coupling assembly comprises two centrally bored cylindrical shaped pressure flanges 42, 43 preferably of stainless steel interconnected by means of a flexible bellows portion 44 of monel or the like. End coupler sections 45, 46 serve to couple cooling fluid to the annular space 34 and the collector cooler assembly through ports 47, 48. Fluid coupling ports 49, 50 serve as exit and entrance ports, respectively, for the tube package.

Two types of cooling fins are located within collector cooler assembly 36. The two end sections of the cooler assembly have a plurality of annular coolings fins 51 brazed to the core 37. Fins 51 form a low velocity, low pressure cooling section. A high velocity, high pressure cooling section comprising fins 52 is positioned between the two end sections. Fins 51 are annular rings of copper or the like having their peripheral edges spaced from the shell 40 preferably A of the radial distance between shell 40 and core 37. This space allows the cooling liquid in the end sections to flow simultaneously between the fins forming each of the end sections as shown by the arrows denoting fluid transfer in the system.

Pins 52 are interdigitally arranged so as to pass the cooling fluid along a meander path between adjacent fins as denoted by the arrows. Fins 52 which are asymmetrical with respect to core 37 alternately seal either the upper or lower half of the cooling space between core 37 and shell 40 and approximately of the respective other half of the cooling space. Since the coOling fluid in the intermediate section is limited to a constricted passage between adjacent fins 52, the fluid pressure and velocity in this section will be proportionately increased by approximately a multiple equal to the number of fluid passages in the end section fed by port 43.

In operation, suitable fluid pumping apparatus is interconnected between ports 49 and 50 and serves to pump a cooling fluid such as oil from port 50 through annular space 34 to port 47, through coupler assembly 41 to port 48 and thence successively unidirectionally through the relatively low pressure drop end section 71, of the cooler assembly; oppositely directed through adjacent fins in the high pressure drop intermediate section 72 and unidirectionally through the relatively low pressure drop end section 73 and out through port 49 to the pumping apparatus.

The above collector cooling system permits limiting the overall tube package pressure drop to a predetermined minimum level while simultaneously utilizing an intermediate high pressure drop, high velocity section which is far more efficient in the rate of heat transfer from the fins surfaces to the fluid because of the higher fluid velocity than the low pressure end sections. This permits a considerable reduction in the number of fins required for a given rate of cooling and thus a considerable saving in overall length.

A major advantage in limiting the overall pressure drop between ports 49, :50, or the tube package, is that a considerable saving in weight is achieved since the smaller the flow rate and total pressure drop across the tub package, the smaller the size of the pumping apparatus. This, of course, is advantageous in any airborne system. The differential pressures across the tube package permit monitoring of the fluid pressure by any well known technique and thus can provide a continuous indication of fluid flow. It is to be noted that the major portion of the collector cooling system could be designed as a high pressure, high velocity section and that the first and third cooling sections, 71, 73 would therefore be designed as high pressure sections. This, of course, would compromise weight for the pumping apparatus but would reduce collector length.

The flexible bellows coupler 44 allows operation of the tube package under both extreme and normal environmental temperature and pressure conditions without cracking or leakage occurring in the cooling system because of differential thermal expansion between the focus ing section and the collector and collector cooling sections.

advantageously be utilized to support a single slow wave circuit such as a helix employed in a backward wave oscillator. In this case the glaze would be applied at the collector end and the RF. section and securing tabs at the gun end or R.F. output end where developed backward wave power is at a maximum. It is also to be noted that the cooling techniques employed herein may equally advantageously be employed in other electron discharge devices besides the traveling wave type.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A high frequency electron discharge device comprising,

(a) electron gun means for generating and directing an electron beam along a predetermined path, within said device,

(b) collector means for collecting said electron beam disposed at the end of said predetermined path,

(c) first and second spaced-apart slow wave circuits positioned in axial alignment along said 'path between the gun and collector,

(d) a first plurality of elongated dielectric rods positioned around and extending along said first slow wave circuit for supporting said first circuit in the device, and

(e) a second plurality of elongated dielectric rods positioned around and extending along said second slow wave circuit for supporting said second circuit in the device,

(f) said first slow wave circuit fixedly attached to said first plurality of elongated dielectric rods only at one end portion of said first slow wave circuit and,

(g) said second slow wave circuit fixedly attached to said second plurality of elongated dielectric rods only at one end portion of said second slow wave circuit, the other ends of said slow wave circuits being free to move relative to the associated support rods,

(h) said first slow wave circuit being a helix which is glazed to said plurality of support rods only at the end portions of said first helix furthest removed from said electron gun means,

(i) said second slow wave circuit being a helix which is glazed to said plurality of support rods only at the end portions of said second helix furthest removed from said collector means,

(j) a main body shell surrounding said first and said second helices and said first and said second plurality of elongated dielectric rods, said main body shell forming a portion of a vacuum tight enclosure about said first and said second helix circuits and said first and said second plurality of elongated dielectric rods,

(k) magnetic beam focusing means surrounding said main body shell and spaced therefrom along the length of said shell, and

(l) a plurality of minute, generally spherical shaped heat conductive members disposed between said main body shell and said focusing means.

2. The device as defined in claim 1 and further comprising,

(a) first cooling assembly means positioned around said focusing means,

(b) second cooling assembly means positioned around said collector means, and

(c) fluid coupling means interconnecting said first cooling assembly means and said second cooling assembly means, said fluid coupling means having a portion thereof made of flexible material whereby differential expansion of said first cooling assembly means relative to said second cooling assembly means will be taken up by said flexible material.

3. The device as defined in claim 2 wherein said sec- 0nd cooling assembly means comprises,

(a) a first cooling section,

(b) an intermediate cooling section coupled to said first cooling section, and

(c) a third cooling section coupled to said intermediate cooling section and wherein said first, intermediate and third cooling sections are adapted and arranged such that for a continuous fluid flow between said first, intermediate and third cooling sections, fluid velocity and fluid pressure drop in said intermediate section is greater than in said first cooling section and said third cooling section.

4. An electron discharge device comprising,

(a) an electron gun assembly, a collector assembly,

(b) and a main body shell disposed between and connected to said electron gun assembly and said collector assembly to form a vacuum envelope,

(c) focusing means surrounding said main body shell and spaced therefrom,

(d) and a plurality of separate minute heat conductive particles disposed in the space between said main body shell and said focusing means, said plurality of separate particles forming a non-integral heat conductive separable mass for facilitating heat flow between said main body shell and said focusing means.

5. An electron discharge device comprising,

(a) an electron gun assembly, a collector assembly,

(b) and a main body shell disposed between and connected to said electron gun assembly and said collector assembly to form a vacuum envelope,

(c) focusing means surrounding said main body shell and spaced therefrom,

(d) and a plurality of separate minute heat conductive particles disposed in the space between said main body shell and said focusing means,

(e) first fluid cooling means surrounding said focusing means,

(f) second fluid cooling means surrounding said collector means,

(g) and flexible fluid coupler means interconnecting said first and said second fluid cooling means.

6. The device as defined in claim 5 wherein said second cooling means comprises:

(a) a first cooling section (b) a second cooling section operatively connected to said first cooling section, and wherein said first and second cooling sections are adapted and arranged such that a continuous fluid flow through said sections will flow at a greater velocity and undergo a greater pressure drop in the second cooling section than in the first cooling section.

7. The device as defined in claim 5 wherein said second fluid cooling means comprises,

(a) a first cooling section (b) an intermediate cooling section operatively connected to said first cooling section (c) a third cooling section operatively connected to said intermediate cooling section, and wherein said first, intermediate and third cooling sections are adapted and arranged such that a continuous fluid flow through said sections will flow at a greater ve :locity and undergo a greater pressure drop in the intermediate cooling section than in the first and third cooling sections.

8. A high frequency electron discharge device compris- (a) an electron gun and a collector member positioned at opposite ends of a predetermined path for defining a path of flow for an electron beam,

(b) a collector cooler assembly mounted on said collector member comprising (1) a first cooling section,

For example, tube starting conditions may be as low as 50 C. below zero. Upon commencing tube operation at such a temperature the solenoid section will expand far less than the collector and tube main body portions thus causing differential expansion between the sections which is taken up by the bellows section.

In order to transfer heat as rapidly as possible from the main body of the tube to minimize R.F. degradation, a unique heat transfer technique is employed in the present invention wherein a plurality of relatively minute pellets or spherical shaped balls 53 are disposed between the main body and the interior surface of the focusing means as shown in FIGS. 1 and 4. A fairly small space of perhaps of an inch will normally exist between the interior of the focusing means and the exterior of the main body due to the necessity of providing clearance for the enlarged collector end portion 20 of the tube, the RJF. conductors 22 and the like. Furthermore, since the mechanical and magnetic axis of the focusing means are seldom if ever coincident, a clearance space such as 30 is desired for purposes of adjustment whereby the electron beam axis can be aligned with the magnetic axis of the focusing means in order to obtain uniform focusing of the beam. This clearance space 30 is, if simply air, undesirable since it impedes rapid and eflicient heat transfer away from the tube main body as mentioned previously. A molten fill material could be poured in this space but is extremely difii-cult to handle and presents a myriad of other problems. For example, it prevents ease of disassembly of the tube from the focusing section for repair purposes not to mention the problems involved with selecting a metal fill which has good heat transfer characteristics coupled with a very low melting point that is additionally capable of being handled in an air atmosphere without danger to personnel and equipment and the tube itself. The utilization of minute pellets or spherical shaped balls, either hollow or solid, preferably of the order of A of an inch in diameter and of such materials as aluminum or copper has provided an excellent solution to the above problems.

The tube is simply inserted within the focusing means, secured by means of flange 26 and inverted. The pellets can then be poured in from the gun end and by slightly shaking the tube package or by means of tamping, the balls are firmly packed between the focusing structure and main body. After packing, the end sealant 19 may be applied. The balls provide excellent heat transfer characteristics, low thermal resistance, in addition to being very light in weight even if solid and obviously much lighter if hollow. Furthermore, assembly and disassembly problems are greatly simplified and the overall tube package is greatly ri-gidified and capable of withstanding severe vibration without damage to the tube as previously pointed out.

It is to be understood that the silicone rubber mass 19 such as RTV-60 or the like could be eliminated and RTV-60 or the like positioned between the solenoid and end cap mating surfaces in order to obtain a gas tight seal. A non-tacky, removable insulating material could advantageously replace the silicone rubber mass 19 thereby facilitating field replacement of the tube.

As mentioned previously, adequate supporting techniques for slow wave structures such as the helix and helix derived circuits are constantly being sought. Prior art techniques are generally found Wanting at higher powers of operation, as for example, in the vicinity of 400 'watts developed power for a helix structure when coupling of R.F. energy to the glaze employed to secure the helix to support rods is of such magnitude as to cause vaporization and destruction of glazed joints along the helix and especially at the RP. output end. In addition, power is lost through coupling along the entire extent of the helix to the glazed joints which may not cause vaporization at the selected power level of operation but which is nevertheless wasted and, since it increases as a direct function of the power level, it is extremely undesirable.

Further problems are encountered in differential expansion problems between the helix and support rods and the tube body or shell which, as pointed out previously, result in cracking and breaking of the R.F. leads to the helix. The present invention solves these problems by utilizing severed support rods 12 and a severed helix 9, 10 and by employing glaze 12 only at the central end portion of the helix sections and allowing frictional contact over the remainder of the helix between the helix and support rods. This minimizes R.F. losses coupling to the glaze and further permits differential thermal expansion between the tube main body and the helix and support rods without crackage of the R.F. leads and without deformation of the helix and consequent change of the pitch between turns which would result in a change in tube operating characteristics.

Cylindrical R.F. matching sections 54 of stainless steel or the like having a plurality of spaced slots 55 partially extending along the length thereof are secured in the opposite ends of the barrel 11. An additional slot 56 extending along the entire length of the R.F. section 54 is also provided to accommodate the R.F. leads 57, 58 extending from the helix. Tabs 60, 61, preferably of tantalum, are spotwelded or otherwise suitably secured to the main body sleeve 11 and the R.F. matching sections 54 as shown to securely fix the location of the support rods, helix and R.F. matching sections within the tube main body 11. Each support rod is provided with a reduced portion 62 at the ends thereof. The helix sections are glazed to the inner ends of the support rods 12 and U- shaped tabs 64 of tantalum or the like fixedly placed within the reduced portions 62 of rods 12 and the assembled sections then positioned within the R.F. matching sections 54. The outer ends of the support rods are slid into the R.F. matching sections until they abut against the back walls 63 of the slots 55 and then the U-shaped tabs 64 are bent into contact with and spot welded to the inner surface of R.F. matching section 54.

The resulting supporting structure allows differential thermal expansion between the tub main body and the helix assembly without any distortion of thte helix since the clearance space 66 between the rods allows expansion of contraction of the helix and rods relative to the tube main body 11 while simultaneously maintaining a fixed relation therebetween at the R.F. input and output coupling joints. An absence of glaze at the output R.F. coupler section eleminates R.F. degradiation due to coupling of the R.F. to the glaze at this point of highest power development on the slow wave structure.

Since the operation of severed helix type traveling wave tubes is generally so well known in the art, the theory of operation of the wave tube shown in the drawings and described above will not be repeated here. A typical helix traveling wave tube employing the supporting and cooling techniques of the present invention developed approximately 500 watts power output in the L-band range with an average gain of around 30 db without vaporization or melting of the glazed joints or cracking of the R.F. leads to the helix.

A flow rate of 1.5 gal/min. of oil fluid was handled by the cooling system on an exemplary tube employing the cooling techniques of the present invention and dissipated over 1300 watts out of approximately 1800 watts input power to the tube showing the adequacy of the cooling system. The above developed power and flow rates are given by way of example and are not to be construed as limiting parameters.

It is to be understood that the number and positioning of the supporting rods and the type of slow wave structure supported thereby may be varied without leaving the scope of the invention as well as the particular material, shape and size of the balls or pellets. It is likewise to be understood that the slow wave circuit supporting technique can (2) an intermediate cooling section operatively connected to said first cooling section, and (3) a third cooling section operatively connected to said intermediate cooling section, and wherein said first, intermediate and third cooling sections are adapted and arranged such that a continuous fluid flow through said sections will flow at a greater velocity and undergo a greater pressure drop in the intermediate cooling section than in the first and third cooling sections, said first cooling section comprising a plurality of spaced cooling fins adapted and arranged such that fluid flow between adjacent fins is unidirectional, said intermediate cooling section comprising a plurality of spaced cooling fins adapted and arranged such that fluid flow between said fins is oppositely directed between adjacent fins, and said third cooling section comprising a plurality of spaced cooling fins adapted and arranged such that fluid flow between adjacent fins is unidirectional. 9. A high frequency electron discharge assembly comprising,

(a) a high frequency tube having an electron gun, tube main body shell and collector operatively connected to each other,

(b) focusing means surrounding said high frequency tube, said focusing means being adapted and arranged relative to said tube such that a clearance space occurs between the external surface of said tube and the internal surface of said focusing means, and

(c) a plurality of separate, minute, thermally conductive cooling members disposed within said clearance space and packed therein such that a low thermal resistive path occurs between said tube and said focusing means, said plurality of separate cooling members forming a non-integral heat conductive separable mass for facilitating heat flow between said main body shell and said focusing means.

10. A high frequency electron discharge assembly comprising,

(a) a high frequency tube having an electron gun, tube main body shell and collector operatively connected to each other,

(b) focusing means surrounding said high frequency tube, said focusing means being adapted and arranged relative to said tube such that a clearance space occurs between the external surface of said tube and the internal surface of said focusing means, and

(c) a plurality of separate, minute, thermally conductive cooling members disposed within said clearance prising,

(a) a high frequency tube having an electron gun, tube main body shell and collector operatively connected to each other,

(b) focusing means surrounding said high frequency tube, said focusing means being adapted and arranged relative to said tube such that a clearance space occurs between the external surface of said tube and the internal surface of said focusing means, and

(c) a plurality of separate, minute, thermally conductive cooling members disposed within said clearance space and packed therein such that a low thermal resistive path occurs between said tube and said focusing means, said minute thermally conductive cooling members being hollow, generally spherical shaped metallic balls.

12. An electron discharge device comprising (a) a tube having an electron beam forming and collecting means and an RF. interaction circuit therein,

(b) and thermally conducting means surrounding said tube comprising a plurality of minute, thermally conductive members packed around said tube, said plurality of minute, thermally conductive members forming a non-integral heat conductive separable mass for facilitating heat flow between said tube and any surrounding structure.

13. An electron discharge device comprising,

(a) a tube having an electron beam forming and collecting means and an RF. interaction circuit therein,

(b) and thermally conducting means surrounding said tube comprising a plurality of minute, thermally conductive members packed around said tube, said minute, thermally conductive members being generally spherical shaped and having diameters approximating of an inch.

References Cited by the Examiner UNITED STATES PATENTS 2,843,789 7/1958 Klein et al. 315 -3.5 2,922,919 1/1960 Brock 315-36 3,114,857 12/1963 Fokker 3l53.5

HERMAN KARL SAALBACH, Primary Examiner.

HERMAN KARL SAALBACH, Examiner. E. LIEBERMAN, R. D. COHN, Assistant Examiners. 

1. A HIGH FREQUENCY ELECTRON DISCHARGE DEVICE COMPRISING, (A) ELECTRON GUN MEANS FOR GENERATING AND DIRECTING AN ELECTRON BEAM ALONG A PREDETERMINED PATH, WITHIN SAID DEVICE, (B) COLLECTOR MEANS FOR COLLECTING SAID ELECTRON BEAM DISPOSED AT THE END OF SAID PREDETERMINED PATH, (C) FIRST AND SECOND SPACED-APART SLOW WAVE CIRCUITS POSITIONED IN AXIAL ALIGNMENT ALONG SAID PATH BETWEEN THE GUN AND COLLECTOR, (D) A FIRST PLURALITY OF ELONGATED DIELECTRIC RODS POSITIONED AROUND AND EXTENDING ALONG SAID FIRST SLOW WAVE CIRCUIT FOR SUPPORTING SAID FIRST CIRCUIT IN THE DEVICE, AND (E) A SECOND PLURALITY OF ELONGATED DIELECTRIC RODS POSITIONED AROUND AND EXTENDING ALONG SAID SECOND SLOW WAVE CIRCUIT FOR SUPPORTING SAID SECOND CIRCUIT IN THE DEVICE, (F) SAID FIRST SLOW WAVE CIRCUIT FIXEDLY ATTACHED TO SAID FIRST PLURALITY OF ELONGATED DIELECTRIC RODS ONLY AT ONE END PORTION OF SAID FIRST SLOW WAVE CIRCUIT AND, (G) SAID SECOND SLOW WAVE CIRCUIT FIXEDLY ATTACHED TO SAID SECOND PLURALITY OF ELONGATED DIELECTRIC RODS ONLY AT ONE END PORTION OF SAID SECOND SLOW WAVE CIRCUIT, THE OTHER ENDS OF SAID SLOW WAVE CIRCUITS BEING FREE TO MOVE RELATIVE TO THE ASSOCIATED SUPPORT RODS, (H) SAID FIRST SLOW WAVE CIRCUIT BEING A HELIX WHICH IS GLAZED TO SAID PLURALITY OF SUPPORT RODS ONLY AT THE END PORTIONS OF SAID FIRST HELIX FURTHEST REMOVED FROM SAID ELECTRON GUN MEANS, (I) SAID SECOND SLOW WAVE CIRCUIT BEING A HELIX WHICH IS GLAZED TO SAID PLURALITY OF SUPPORT RODS ONLY AT THE END PORTIONS OF SAID SECOND HELIX FURTHEST REMOVED FROM SAID COLLECTOR MEANS, (J) A MAIN BODY SHELL SURROUNDING SAID FIRST AND SAID SECOND HELICES AND SAID FIRST AND SAID SECOND PLURALITY OF ELONGATED DIELECTRIC RODS, SAID MAIN BODY SHELL FORMING A PORTION OF A VACUUM TIGHT ENCLOSURE ABOUT SAID FIRST AND SAID SECOND HELIX CIRCUITS AND SAID FIRST AND SAID SECOND PLURALITY OF ELONGATED DIELECTRIC RODS, (K) MAGNETIC BEAM FOCUSING MEANS SURROUNDING SAID MAIN BODY SHELL AND SPACED THEREFROM ALONG THE LENGTH OF SAID SHELL, AND (L) A PLURALITY OF MINUTE, GENERALLY SPHERICAL SHAPED HEAT CONDUCTIVE MEMBERS DISPOSED BETWEEN SAID MAIN BODY SHELL AND SAID FOCUSING MEANS. 